BOSTON (WHDH) -- Workers were evacuated from a building at Logan Airport because of a gas odor on Tuesday evening.

Officials said high levels of carbon monoxide started filling an American Airlines cargo building on Harborside Drive.

Employees inside started getting nauseated. Officials said about 25 employees evacuated the building. Five of those employees were taken to hospitals complaining of nausea and lightheadedness.

Boston paramedics said those symptoms appeared to be minor.

Authorities said the cause of the odor may have been a faulty forklift that spewed fumes.

“Logan fire believes it’s a faulty forklift that was being operated inside the building. We’re not sure exactly yet,” said Deputy Supt. Steve McHugh of Boston EMS. “Any time a combustion engine is running inside a building, if it’s not running effectively, it can give off carbon monoxide.”

The building has been ventilated.